linux/net/ipv4/tcp_timer.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		Implementation of the Transmission Control Protocol(TCP).
 *
 * Authors:	Ross Biro
 *		Fred N. van Kempen, <[email protected]>
 *		Mark Evans, <[email protected]>
 *		Corey Minyard <[email protected]>
 *		Florian La Roche, <[email protected]>
 *		Charles Hedrick, <[email protected]>
 *		Linus Torvalds, <[email protected]>
 *		Alan Cox, <[email protected]>
 *		Matthew Dillon, <[email protected]>
 *		Arnt Gulbrandsen, <[email protected]>
 *		Jorge Cwik, <[email protected]>
 */

#include <linux/module.h>
#include <linux/gfp.h>
#include <net/tcp.h>
#include <net/rstreason.h>

static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
{ … }

u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
{ … }

/**
 *  tcp_write_err() - close socket and save error info
 *  @sk:  The socket the error has appeared on.
 *
 *  Returns: Nothing (void)
 */

static void tcp_write_err(struct sock *sk)
{ … }

/**
 *  tcp_out_of_resources() - Close socket if out of resources
 *  @sk:        pointer to current socket
 *  @do_reset:  send a last packet with reset flag
 *
 *  Do not allow orphaned sockets to eat all our resources.
 *  This is direct violation of TCP specs, but it is required
 *  to prevent DoS attacks. It is called when a retransmission timeout
 *  or zero probe timeout occurs on orphaned socket.
 *
 *  Also close if our net namespace is exiting; in that case there is no
 *  hope of ever communicating again since all netns interfaces are already
 *  down (or about to be down), and we need to release our dst references,
 *  which have been moved to the netns loopback interface, so the namespace
 *  can finish exiting.  This condition is only possible if we are a kernel
 *  socket, as those do not hold references to the namespace.
 *
 *  Criteria is still not confirmed experimentally and may change.
 *  We kill the socket, if:
 *  1. If number of orphaned sockets exceeds an administratively configured
 *     limit.
 *  2. If we have strong memory pressure.
 *  3. If our net namespace is exiting.
 */
static int tcp_out_of_resources(struct sock *sk, bool do_reset)
{ … }

/**
 *  tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
 *  @sk:    Pointer to the current socket.
 *  @alive: bool, socket alive state
 */
static int tcp_orphan_retries(struct sock *sk, bool alive)
{ … }

static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
{ … }

static unsigned int tcp_model_timeout(struct sock *sk,
				      unsigned int boundary,
				      unsigned int rto_base)
{ … }
/**
 *  retransmits_timed_out() - returns true if this connection has timed out
 *  @sk:       The current socket
 *  @boundary: max number of retransmissions
 *  @timeout:  A custom timeout value.
 *             If set to 0 the default timeout is calculated and used.
 *             Using TCP_RTO_MIN and the number of unsuccessful retransmits.
 *
 * The default "timeout" value this function can calculate and use
 * is equivalent to the timeout of a TCP Connection
 * after "boundary" unsuccessful, exponentially backed-off
 * retransmissions with an initial RTO of TCP_RTO_MIN.
 */
static bool retransmits_timed_out(struct sock *sk,
				  unsigned int boundary,
				  unsigned int timeout)
{ … }

/* A write timeout has occurred. Process the after effects. */
static int tcp_write_timeout(struct sock *sk)
{ … }

/* Called with BH disabled */
void tcp_delack_timer_handler(struct sock *sk)
{ … }


/**
 *  tcp_delack_timer() - The TCP delayed ACK timeout handler
 *  @t:  Pointer to the timer. (gets casted to struct sock *)
 *
 *  This function gets (indirectly) called when the kernel timer for a TCP packet
 *  of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
 *
 *  Returns: Nothing (void)
 */
static void tcp_delack_timer(struct timer_list *t)
{ … }

static void tcp_probe_timer(struct sock *sk)
{ … }

static void tcp_update_rto_stats(struct sock *sk)
{ … }

/*
 *	Timer for Fast Open socket to retransmit SYNACK. Note that the
 *	sk here is the child socket, not the parent (listener) socket.
 */
static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
{ … }

static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
				     const struct sk_buff *skb,
				     u32 rtx_delta)
{ … }

/**
 *  tcp_retransmit_timer() - The TCP retransmit timeout handler
 *  @sk:  Pointer to the current socket.
 *
 *  This function gets called when the kernel timer for a TCP packet
 *  of this socket expires.
 *
 *  It handles retransmission, timer adjustment and other necessary measures.
 *
 *  Returns: Nothing (void)
 */
void tcp_retransmit_timer(struct sock *sk)
{ … }

/* Called with bottom-half processing disabled.
   Called by tcp_write_timer() */
void tcp_write_timer_handler(struct sock *sk)
{ … }

static void tcp_write_timer(struct timer_list *t)
{ … }

void tcp_syn_ack_timeout(const struct request_sock *req)
{ … }
EXPORT_SYMBOL(…);

void tcp_set_keepalive(struct sock *sk, int val)
{ … }
EXPORT_SYMBOL_GPL(…);


static void tcp_keepalive_timer (struct timer_list *t)
{ … }

static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer)
{ … }

void tcp_init_xmit_timers(struct sock *sk)
{ … }